How to make an object appear to be buried in sand?
A result like this can be obtained using the particle system (without physics) and vertex weighting in cycles.





Steps


Create a sand surface object and a watch object. You can partially cover the watch in sand. Adding modifiers to the sand to displace with a rough texture can simplify creating this surface. If you render them, you should get something like this:





Add an icosphere to act as a grain of sand. Move it out of the camera view. Add a shader to the grain of sand which changes colors and transparency depending on the particle number. The idea is to use the particle number to set the color and transparency of each sand grain, so the result is varied. The shader is shown below:





Add a particle system to the sand surface. Set physics to 'No'. Set all particles to emit at time 1. The example image was generated with about 250K particles. Since physics isn't used, this runs reasonably fast.




If this is rendered, the results should look something like this, looking like it was dropped on the sand.




To partially cover the watch with sand, use vertex weights. This requires going into 'weight paint' and using the brush to indicate where you want the sand grains to overlay the watch. For the image above, this weight painting was used. The red color indicates where sand grains will be dense and deep blue indicates where the sand will be absent.





Set up the sand particle system on the watch. However, to control where the grains go, use the vertext groups and specify the 'group' vertext group. This will refer to the vertext weights generated in step 4.





Render the image! Since no physics simulation is required, the rendering should occur relatively fast. On a 2 core, 1.5 GHz machine, 4Gb ram, with >250K sand particles, the image rendered in less than a minute.






Download the blend file here: